1. Field of the Invention
This invention relates to torque arm assemblies for backstopping clutches and, more particularly, to torque arm assemblies that can facilitate load sharing among multiple backstop assemblies within a larger system and/or allow for controlled release of load or tension on the backstop.
2. Disclosure of Related Art
In many motor driven systems, it is desirable to prevent or limit movement of system components in one direction. For example, and with reference to FIG. 1, mining operations typically use inclined conveyors 10 to convey material 12 to a surface location or other outlet. It is desirable to prevent or limit reverse movement of the conveyor 10 in the event of a loss of power or a failure of a driveline component such as the motor 14 or motors, gearboxes or couplings in order to prevent material 12 from moving backwards on the conveyor 10 and causing damage to the system and significant injuries to personnel operating the system.
Backstopping clutches 16 are typically used to prevent reverse rotation of rotating system components. Referring to FIGS. 1 and 2, each clutch 16 includes an inner race 18 that is mounted to a shaft 20 driven by one or more motors 14 for rotation with the shaft 20 about a rotational axis 22. An outer race 24 is disposed radially outward of the inner race 18 and is generally fixed against rotation. A plurality of rollers 26 are disposed radially between the inner and outer races 18, 24 and are urged into engagement with the races 18, 24 by springs 28. The rollers 26 and/or a groove 30 in outer race 24 are shaped such that when the motor 14 drives the shaft 20 and inner race 18 in one rotational direction, the rollers 26 assume a first position permitting relative rotation of the inner and outer races 18, 24. When the driven shaft 20 and inner race 18 are driven in the opposite rotational direction (e.g. by the force of the load of material 12 upon failure of motor 14), the rollers 26 assume a second position and forcefully engage the inner and outer races 18, 24 and prevent the inner race 18 and driven shaft 20 from rotating relative to the fixed outer race 24.
Referring again to FIG. 1, the outer race 24 of each backstopping clutch 16 may be fixed against rotation using a torque arm assembly 32. The assembly 32 includes a head 34 that is connected to the outer race 24 of the clutch. An arm 36 extends from the head and is fixed at a remote end 38 to a stationary structure 39 (e.g., support structure for the conveyor 10). Arm 36 is integral with head 34 or rigidly coupled to head 34.
Conventional torque arm assemblies such as assembly 32 have several disadvantages. The rigid nature of the torque arm assembly 32 results in instantaneous engagement of the outer and inner races 18, 24 of clutch 16 and therefore requires that clutch 16 be designed to absorb the maximum load on the conveyor 10. Accordingly, the clutches 16 are relatively expensive. This is particularly problematic in systems incorporating multiple motors 14 and clutches 16. In large conveyor systems or in other applications, multiple backstopping clutches 16 may be disposed on a single shaft 20 and/or clutches may be required for multiple motor driven shafts 20. There is also no mechanism for indicating the load on clutch 16 and no mechanism for releasing load or tension on clutch 16. Some torque arm assemblies have been devised to enable load sharing among multiple clutches in large systems. Referring to FIG. 1, these type of assemblies have typically employed a rubber pad, spring, or hydraulic cylinder seated between end 36 of the arm and the stationary structure 39. Although these assemblies enable some form of load sharing by delaying engagement of the inner and outer races 18, 24 of the clutch 16, the assemblies require costly modifications to the support structure 39. Further, the assemblies do not provide means for lead sensing or releasing load or tension on the clutch 16.
The inventor herein has recognized a need for a torque arm assembly for a backstopping clutch that will minimize and/or eliminate one or more of the above-identified deficiencies.